#include <stdio.h>

int sum(int start, int count);

int main() {
    int n, result = 0;
    scanf("%d", &n);
    for(int i = 1; i <= n; i++){
        result += sum(i, i + 1);
    }
    printf("sum=%d", result);
    return 0;
}

int sum(int start, int count){
    int result = start;
    for (int i = 1; i < count; i++){
        start++;
        result += start;

    }
    return result;
}
